The alkylation of benzene with olefins produces a variety of alkylbenzene compounds that have various commercial uses. Examples include the alkylation of benzene with olefins having 8 to 16 carbons for the production intermediate compounds in the manufacture of detergents. The alkylbenzenes are sometimes referred to as phenylalkanes, and are produces as a commodity in amounts between 50,000 and 200,000 metric tonnes per year, at a large scale facility. The alkylation process comprises reacting benzene with an olefin in the presence of a catalyst at elevated temperatures. The catalysts can be homogeneous or heterogeneous catalysts such as hydrogen fluoride, aluminum chloride, silica alumina, or zeolitic catalysts.
The desired alkylated compounds are monoalkylated aromatic compounds. Two common reactions for producing monoalkylated aromatic compounds are alkylation of aromatic compounds such as benzene, and transalkylation of polyalkylated aromatic compounds. Monoalkylated aromatic compounds include linear alkylbenzenes (LAB), which are used to form linear alkylbenzene sulfonates (LABS), a common compound used in detergents, and which are manufactured from linear alkylbenzenes. One aspect of benzene alkylation has been the use of high benzene to olefin ratios for the production of alkylbenzene production. The transalkylation process reacts the polyalkylated aromatic compound with benzene to form a monoalkylated product. Both the alkylation and transalkylation processes involve the use of benzene in a relatively high molar ratio with respect the olefin or polyalkylated aromatic compound.
Currently, monoalkylated benzenes are desired, and polyalkylated benzenes are by-products that need to be removed or need to be recycled to try and produce more monoalkylated benzenes. The method of reducing the amount of polyalkylated benzenes is to increase the benzene to olefin ratio. The other method of reducing polyalkylated benzenes is to pass the polyalkylbenzenes through a transalkylation reactor. However, the industry is striving to reduce the benzene to olefin ratio, and the usual method is to use many small beds with decreasing ratios as the benzene and olefins pass through successive beds. The cost of producing a pure benzene stream is expensive, and the cost of separating and recycling benzene is expensive and energy intensive.
Methods of improving the recovery and usage of benzene can result in substantial savings in energy and expense.